doc/go1.17: remove TODO for ports section

I'm not aware of anything more to mention for ports.

Change-Id: I686df8a230a55ad7f4c5eae43ca27f85fad9dd84
Reviewed-on: https://go-review.googlesource.com/c/go/+/326409


Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>